DE2658191C2 - Process for the production of maleic anhydride - Google Patents

Description

¹⁰ a) a crystalline phosphorus-vanadium mixed oxide catalyst is used as the catalyst, which contains pentavalent phosphorus, vanadium and oxygen, the vanadium having an average between about +3.9 and +4.6 and the oxide having a phosphorus: vanadium atomic ratio between about 0.9 to 1.8: 1 and a true surface area of about 7 to 50 m '/ g,

b) the maleic anhydride is removed from the reactor outlet to obtain the low-malelic anhydride outlet ¹⁵ by countercurrent to the reactor outlet with an organic absorbent

Brings into contact whereby the maleic anhydride is absorbed into the organic absorbent will,

c) the malelic anhydride, C ^ hydrocarbon, nitrogen, oxygen and acrylic, vinegar or Maleic acid or mixtures of these acids containing spout with water or an aqueous alkaline

See solution to obtain a purified recycle stream containing less than 100 ppm acids washed and

d) this purified stream is returned to the reactor.

The oxidation of hydrocarbons to maleic anhydride is known. Benzene, butene and n-bulane, for example, are used as starting materials. In US-PS 31 56 705, 31 56 706, 31 56 707, 32 38 254, 32 55 211, 32 55 212, 32 55 213, 32 88 721, 33 51 565 and 33 85 796 vanadium-phosphorus oxide catalysts ¹¹¹ for the oxidation of butene to maleic anhydride.

The US-PS 34 78 063 describes the oxidation of olefinically unsaturated hydrocarbons with a Catalyst containing vanadium and phosphorus oxides, the amount of phosphorus oxide being at least the Is twice the amount of vanadium oxide and the catalyst is at least one other oxide of chromium, Elsen, cobalt or nickel and is preferably located on a carrier. It is stated that the • The catalyst can have a surface area of 1 to 100 mVg.

The US-PS 32 93 268 describes a vanadium phosphorus oxide catalyst for the oxidation of butane to maleic anhydride. The surface of the catalyst is not discussed in this reference. Like in In the case of the aforementioned US Pat. No. 3,778,063, the catalyst is prepared by an aqueous solution method.

· »<> The US-PS 38 64 280 describes a vanadium-phosphorus mash oxide catalyst with a true surface Il from 7 to 50 mVg. This catalyst can be produced using an organic medium.

; ". · The return of unreacted components to a reactor is known and is also used in

| "Carried out various procedures.

H In "Oxidation οΓ Butane to Maleic Anhydride", IEC Vol. 2, No. 1, March 1963, is rarely 57 to 60

j | - »s stated that in a process for converting butane to maleic anhydride unconverted ψ butane can be fed back into the reactor. According to this reference, the reaction

P honing carried out in sections, the maleic anhydride being separated off between the reactors.

k ' In this case, partially converted butane is fed from the first reactor into the second reactor and so on.

The US-PS 39 04 652 describes the oxidation of η-butane to maleic anhydride using an-

:, Sn enriched! Oxygen, using a recycle stream from the reactor effluent, which the

|; Oxygen concentration decreased throughout the feed to the reactor. It is known that

ψ. Explosive mixtures of butane and oxygen exist, and some oxygen-butane-nitrogen mixtures exist

;,; the explosive area can fall [cf. e.g. Bureau of Mines Bulletin 503 (1952), Figure 35,

jjv page 62 and Bureau of Mines Bulletin 627 (1965), Figure 21, page 33]. According to US-PS 39 04 652 is the

t <[ ^5S reactor charge mixture below explosive (flammable) limits due to the addition of an inert gas,

! -; ■ for example nitrogen, kept to the fresh feed enriched with oxygen.

I The degrees of butane conversion according to US Pat. No. 3,904,652 are 30 to 70% per pass. That doesn’t mean

The butane that is set flows out of the oxidation reactor as part of the reactor drain. The process becomes removal

. processed by maleic anhydride. The maleic anhydride is partially removed from the effluent by cooling

; <> "removed to condense out liquid maleic anhydride. By washing the Danipf / Gas material.

ρ that remains in the condensation stage, the remaining maleic anhydride is removed from the drain.

[I The washing is carried out by contacting the drain with a circulating aqueous maleic acid solution, the

dnc an unspecified amount of fresh water has been added. The malelnic anhydride gaseous The drain is then split into two parts, namely a recycle stream that returns to the reactor

^{IIS is supplied and a purge stream that} is removed from the system.

A disadvantage of the known method, in particular the method known from US Pat. No. 3,9 04,652, is the fact that the catalysts contaminate relatively quickly and are thus deactivated. What this Impurities can be traced back to, was not previously known.

The invention is based on the knowledge that the in the reactor outlet and thus also in the maleic anhydride Circulation stream present acids, such as acetic, acrylic and maleic acid, even in traces of recycling to the reactor contaminate the catalyst and thus the conversion and selectivity deteriorate the procedure. By the inventive method according to the claim, this Prevents deterioration in conversion and selectivity. The method according to the invention enables a reduction in the concentration, in particular of the light acids mentioned, to less than 100 ppm In the circulating stream. Experiments have shown that as little as 300 ppm of light acids in the recycle stream cause considerable damage to the catalyst and significantly reduce the production rate of additional increase light acids.

In US-PS 38 64 280, which corresponds to DE-OS 23 54 372, a process for the production of Maleinsäureani <ydrld by oxidation of η-butane in a reaction zone in the presence of a complex phosphorus-vanadium-oxygen catalyst described. In the case of this reference, too, one was not that Aware of the problems described which are due to the presence of acids in the recycle stream. Accordingly, this US-PS is not the slightest indication that light acids are a have an adverse effect on catalyst activity. The essence of what is described in this US patent Process is the production of maleic anhydride using enriched oxygen. the Amount of light acids fed back into the reactor according to the method of the said US-PS is 1500 ppm and is thus well above 100 ppm. which are still present according to the invention.

The process according to the invention also provides an extremely high yield of maleic anhydride achieved, which goes back to the knowledge gained, that by light acids in the catalytic reaction are generated, the catalysts used are deactivated and accordingly from the recycle gas stream must be removed, which was done for the first time by the invention.

The washing out with water according to step (d) can, for example, be carried out using an absorption column be carried out in which the malelic anhydride drain into countercurrent contact with water is brought, whereby acids are absorbed and removed from this drain before the mulelnic anhydride poor Drain is fed back to the reactor. The water and / or the aqueous basic solution, such as a sodium or calcium hydroxide solution, carbonate solution or carbonate solution must be in such a Amount used sufficient to remove the acids to such an extent that the low-maleic acid effluent fed back into the reactor does not contain more than 100 ppm of the acids. Preferably the washing is carried out to such an extent that the acid content is less than 10 ppm and, in particular, less than 7 ppm.

In addition to the acids, other partially oxidized by-products such as Formaldehyde, removed so that the recycle stream no more than 100 and preferably no more than 10, In particular, it does not contain more than 7 ppm of these partially oxidized by-products.

The specified ppm amounts of acids and partially oxidized by-products relate to the weight, unless stated otherwise. The term “partially oxidized products” is to be understood as meaning all products, apart from the carbon oxides, which _{arise during the complete oxidation of the C 4} hydrocarbon mixture.

In the process according to the invention, it is preferred to feed the maleic anhydride from the reaction outlet A low-malelic anhydride outlet can only be achieved by countercurrent contact of the reactor outlet with an organic absorbent and not using an aqueous malelic anhydride condensation recovery system to win. The maleic anhydride is then removed from the organic absorbent obtained by conventional absorbent stripping methods. Among the appropriate organic Absorbents include benzophenones such as polymethylbenzophenones, e.g. B. Di-, TrI- and Tetramethylbenzophenon. as described in German patent application P 25 10 479.4. Preferred operating conditions for the oxidation reactor are as follows:

Temperature, ⁰ C pressure, kp / cm * space velocity, VHSV)

feed n-butane content, combined fresh + recirculated feed, vol-%

% Run-out directly in the circuit 20 to 95 65 to 90 80

(Remainder of the circulated n-butane effluent after separation from others Outlet gases)

¹ I total volume of gas at 21.1 ⁰ C and I atmosphere per hour per 0.0283 m · 'catalyst volume.

As explained in US Pat. No. 3,846,280, the term "true surface" means as it is used here is used, the surface of the mixed vanadium-phosphorus oxide Maierliils as such, i.e. without Carrier.

The catalysts of US Pat. No. 3,864,280 are particularly suitable for use in the process according to the invention

preferred particularly
preferred most notably
preferred 343 to 510 371 to 454 371 to 427 1.73 to 71.33 2.44 to 4.55 2.79 to 3.84 1,000 to 10,000 2000 to 5000 3500 to 4500 1 to 5 1.5 to 4 2 to 3.5

133.9 to 13,390 133.9 to 3347.5 1 to 25 1 to 10 10 to 49 10 to 26.7 1.03 to 71.33 1.38 to 3.84

Preferred operating conditions for the removal of the acids from the low-malelic anhydride reactor effluent using a water washing process are the following:

particularly preferred

preferred

Feed rate of the water

to feed rate of ¹⁰ maleinsäureanhydridarmen outlet, l / m ³

Countercurrent contact stages, theoretical stages

Fresh water feed temperature ^{, 0 C}

¹⁵ operating pressure, bar

The following examples are used in conjunction with the schematic process flow diagram further explanation of the invention.

2Ii B e I s ρ i e 1 1

Feed butane In line la from 44 kg / hour. fresh feed butane In line 1 and 16 kg / h. recycled butane in line 16 was with about 647 kg / h. fresh air introduced via line 2 and about 2721 kg / hour Recirculated exhaust gas mixed and the mixture introduced into the oxidation reactor 4. Of the

¹ ^ Oxidation reactor consisted of a conventional heat exchanger with a tube-filled catalyst surrounded by a heat transfer fluid (a salt bath). The reaction mixture was oxidized in the presence of a catalyst which had an accelerating effect on the reaction of η-butane with air with the formation of maleic acid anhydride. Preferred catalysts contained mixed oxides of vanadium and phosphorus, in particular those which are mentioned in the aforementioned US Pat. No. 3,864,280, with the preferred

¹¹¹ reaction temperatures were between 371 and 421 ° C.

After the oxidation, the gaseous effluent flowed through line 5 into the absorber 6. About 47 kg / hour. Maleic anhydride were in the organic solvent flowing into the absorber from line 7 absorbed. The gaseous stream, 3380 kg / hour, left the absorber through line 9 at a temperature of ' about 71 ° C, whereupon it was washed in vessel 10 with water. The Solvent-Maieinsäurearihydrld-Strom

- ^1S left the absorber through line 8 to strip off the maleic anhydride and further purify the crude product.

3380 kg / hour residual stream 9 poor in maleic anhydride was in the countercurrent water scrubber 10 under Washed using fresh water to remove the non-absorbed acids. In a typical Single-stage washers remove about 9942 kg / hour. Fresh water about 1.36 to 1.81 kg / hour. weak acids (vinegar,

■ w Acrylic, maleic and traces of butyric acid and similar) and unabsorbed maleic anhydride. The water requirement can be reduced by using a multi-stage washer. The acidity of the 3328 kg / hour Stream 13 is below about 10 ppm, especially about 6 ppm for this type of treatment.

Washout gas, which exited the water scrubber at a temperature of about 38 to 49 ° C, was split into two Streams 3 and 14 split. About 2721 kg / hour this washout gas was compressed and passed through

• »5 line 3 returned to the oxidation reactor, while the remaining 606 kg / hour. Exhaust gas through line 14 for butane recovery in adsorber 15 were performed.

Butane in line 14 was adsorbed into the adsorber by using a recycle operation of multiple beds filled with adsorbents such as activated carbon. 590 kg / hour of the impoverished Exhaust gas mainly containing oxygen, nitrogen and carbon oxides was discharged and that on the Adsorbent adsorbed butane by suitable desorption such as evaporation at about 121 ° C and subsequent Won condensation and phase separation. The recovered butane, 16 kg / hour, was then through Line 16 returned to the reactor.

To reduce the amount of aqueous washout solution and / or to achieve a more complete one Removal of the acids from the circuit part of the reactor outlet is advantageously a solution of Sodium or potassium hydroxide, carbonate or bicarbonate used in water instead of plain water.

Example 2

The procedure of Example 1 was followed using a single-stage washout of the low-maleic anhydride content

ω exhaust gas to remove the weak acids from the circulating flow to the reactor.

The Effects of Acid Contaminants in a reactor charge was in a separate test reactor tested (since the conditions in the main reactor should not be changed) using the same Catalyst as used in the main reactor. The reactant charge to this one The test reactor consisted of an effluent and side stream from streams No. 5 and 13 of FIG. 1, respectively Receiving the test reactor charge from Stream 13, the test reactor was exposed to a washout gas which consisted of butane, oxygen, nitrogen and carbon oxides with only slight traces of weak ones Acids (about 6 ppm). The relative rates obtained for the first attempt (see Experiment No. 1 in below Table I) were used for further comparison.

The further tests consisted of alternately redirecting the test reactor feed to the rare streams from streams 5 and 13 and assessing the behavior of the test reactor for each of these trials.

The behavior of the test reactor under these conditions is shown in Table I. It should be noted that that the presence of acid impurities in the feed immediately affects catalyst activity and selectivity for maleic anhydride formation (cf. Experiment No. 2 in Table I).

This adverse effect was also found to be irreversible in removing the feed contaminants In the following test (cf. Experiment No. 3 in Table I). The degradation of the catalytic converter progresses if this is further treated with an acid-contaminated stream (see experiment no. 4, second treatment with stream No. 5).

The rather surprising result of these experiments is that the presence of acid impurities in the Charging increases the production rate of the weak acids in the subsequent experiments. In one Circulation operation with less effective removal of acid contaminants from the recirculated effluent stream this adverse effect certainly causes a continuous accelerated degradation of the Catalyst performance. It is therefore particularly advantageous to use the weak acids according to the invention Procedure to remove. Further attempts at a synthetic feed that combined butane with containing either acetic acid or acrylic acid in the absence of maleic anhydride, confirm this disadvantageous Effect observed using current S.

Table I.

Effect of acid impurities on catalyst performance in the test reactor

Downstream or side stream of the feed

Relative rates

Butane MA-

Oxidation production

weakness
Acid production

1) Originally used as test reactor feed

Portion of stream 13 (comparative experiment)

2) after the first encounter of the test reactor catalyst with 1 portion of stream 5 *)

3) again feeding the purified stream 13 into the

T? Streactor

4) second meeting with electricity 5 *)

5) again feeding the stream 13 into the test reactor

*) Components of the impurity: MA 1.38% by weight

Acetic acid 660 ppm acrylic acid 330 ppm

100 100 100 65 65 128 91 92 157 61.4 59.7 171 73.8 69.4 214

1 sheet of drawings

Claims (1)

Claim: Process for the production of maleic anhydride from a C ₄ hydrocarbon, namely an η-butane or n-butene coating, in which the Ci hydrocarbon and atmospheric oxygen are fed into a reactor and with a catalyst made of vanadium and phosphorus oxides under the usual reaction conditions including at a temperature of 288 to 538 ° C., maleic anhydride is removed from the reactor outlet, the maleic acid anhydride-poor outlet is washed and returned to the reactor, characterized in that